lkml.org 
[lkml]   [2015]   [Oct]   [19]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH net-next 3/4] bpf: add support for persistent maps/progs
    On 10/19/2015 09:36 AM, Hannes Frederic Sowa wrote:
    > Hi,
    >
    > On Sun, Oct 18, 2015, at 22:59, Alexei Starovoitov wrote:
    >> On 10/18/15 9:49 AM, Daniel Borkmann wrote:
    >>> Okay, I have pushed some rough working proof of concept here:
    >>>
    >>> https://git.breakpoint.cc/cgit/dborkman/net-next.git/log/?h=ebpf-fds-final5
    >>>
    >>> So the idea eventually had to be slightly modified after giving this
    >>> further
    >>> thoughts and is the following:
    >>>
    >>> We have 3 commands (BPF_DEV_CREATE, BPF_DEV_DESTROY, BPF_DEV_CONNECT), and
    >>> related to that a bpf_attr extension with only a single __u32 fd member
    >>> in it.
    >> ...
    >>> The nice thing about it is that you can create/unlink as many as you
    >>> want, but
    >>> when you remove the real device from an application via
    >>> bpf_dev_destroy(fd),
    >>> then all links disappear with it. Just like in the case of a normal
    >>> device driver.
    >>
    >> interesting idea!
    >> What happens if user app creates a dev via bpf_dev_create(), exits and
    >> then admin does rm of that dev ?
    >> Looks like map/prog will leak ?
    >> So the only proper way to delete such cdevs is via bpf_dev_destroy ?
    >
    > The mknod is not the holder but rather the kobject which should be
    > represented in sysfs will be. So you can still get the map major:minor
    > by looking up the /dev file in the correspdonding sysfs directory or I
    > think we should provide a 'unbind' file, which will drop the kobject if
    > the user writes a '1' to it.

    I agree, this could still be done.

    >>> On device creation, the kernel will return the minor number via bpf(2),
    >>> so you
    >>> can access the file easily, f.e. /dev/bpf/bpf_map<minor> resp.
    >>> /dev/bpf/bpf_prog<minor>,
    >>> and then move on with mknod(2) or symlink(2) from there if wished.
    >>
    >> what if admin mknod in that dir with some arbitrary minor ?
    >
    > Basically, -EIO. :)
    >
    >> mknod will succeed, but it won't hold anything?
    >
    > That is right now true for basically all mknod operations, which udev
    > creates.
    >
    >> looks like bpf_dev_connect will handle it gracefully.
    >> So these cdevs should only be created and destroyed via bpf syscall
    >> and only sensible operations on them is open() to get fd and pass
    >> to bpf_dev_connect and symlink. Anything else admin should be
    >> careful not to do. Right?
    >
    > Besides maybe some statistics and other stuff in sysfs directory, no,
    > that is all.
    >
    > Bye,
    > Hannes


    \
     
     \ /
      Last update: 2015-10-19 12:21    [W:5.872 / U:0.264 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site